(1)-3, 4-methylenedioxymethamphetamine (MDMA, ecstasy) is a common drug of abuse that continues to be a public health concern. While the oral route of administration is the most common route used by recreational users, investigations of the reinforcing efficacy and subjective effects of MDMA have rarely used the oral route of MDMA administration. Development of an oral MDMA self-administration model, and a better understanding of how the subjective effects of orally administered MDMA are neurochemically mediated, in a species closely related to humans would significantly enhance our ability to develop pharmacotherapies intended to improve clinical treatment of MDMA abuse. Toward this goal, our first aim is to characterize the relative reinforcing efficacy of orally available MDMA in baboons in two experiments. First, reliable oral self-administration of MDMA will be engendered using a procedure that has been successful in previous studies of psychoactive compounds in baboons. A concentration-response function of orally available MDMA will be compared to vehicle, to d-amphetamine, and to a non-drug oral reinforcer (a fruit drink). In a second experiment, choice procedures will be used to compare multiple concentrations of MDMA to the other reinforcers. These studies will establish the methodology by which reliable, long-term oral MDMA self-administration can be studied experimentally in a nonhuman primate, will determine the range of concentrations across which reinforcement occurs, will determine whether cyclicity in pattern of self-administration develops across days, and will permit comparison to another commonly orally abused stimulant drug, as well as to a preferred non-drug oral reinforcer. Our second aim is to differentiate the discriminative stimulus effects and the neurochemical correlates of a low and a high dose of orally administered MDMA in baboons by use of multiple-dose discrimination procedures. The putatively differential neurochemical changes that occur as a function of lower and higher doses of MDMA administration will be investigated using drug substitution and antagonism testing in baboons trained to discriminate a low or a high dose of MDMA, and then when the baboons are discriminating both doses. We anticipate the discriminative stimulus effects of a low dose of MDMA will differ significantly from those of a high dose of MDMA, as evidenced by the generalization and antagonism profiles for each training dose. These data will be important to our understanding of the extent to which neurochemical mechanisms are mirrored in subjective drug effects in general and for MDMA in particular. The distinguishing features of our proposal are the use of the oral route of MDMA administration under well-controlled laboratory conditions in baboons, and the use of multiple training doses in the investigation of the discriminative stimulus effects of MDMA in baboons. Our proposal will generate data fundamental to the future development of pharmacotherapies for MDMA abuse, thereby contributing to our long-term goal of facilitating treatment of MDMA intoxication, overdose, and use/abuse.